Generally, there has been known an electrostatic coating apparatus which includes, for example, a rotary atomizing head provided on a fore end side of an air motor, a cover member provided in a tubular shape in such a manner as to enshroud outer surfaces of the air motor formed of an electrically insulating material, and a high voltage generator for charging paint particles, which are sprayed by the rotary atomizing head of an atomizer, with a negative high voltage by means of an external electrode assembly (e.g., Patent Document 1: Japanese Patent Laid-Open No. 2001-113207 A, and Patent Document 2: Japanese Patent Laid-Open No. Hei 11-276937 A).
In the electrostatic coating apparatuses described in Patent Documents 1 and 2, a shaping air ring having a plurality of air outlet holes is provided on the rear side of the rotary atomizing head. The air outlet holes of this shaping air ring spurt out shaping air toward a vicinity of a paint releasing edge of the rotary atomizing head. Consequently, the shaping air shears and atomizes the liquid thread of the paint released from the rotary atomizing head, and shapes the spraying pattern of this atomized paint.
With the electrostatic coating apparatus according to the conventional art, electrostatic fields are formed by electric flux lines between the external electrode assembly with the negative high voltage applied thereto and the rotary atomizing head held at earth potential and between the external electrode assembly and a work piece, respectively. In the vicinity of a fore distal end of the external electrode assembly, corona ions are generated by a corona discharge, and a negative ionization zone is formed by these corona ions.
If, in this state, paint is sprayed by the rotary atomizing head which is put in high speed rotation, paint particles sprayed from the rotary atomizing head are electrified by application of a negative high voltage during travel through the ionization zone to become negatively charged paint particles. As a result, the charged paint particles are urged to fly toward the work piece and deposit on surfaces of the work piece which is connected to the earth.
In addition, as an electrostatic coating apparatus according to another conventional art, a construction is known in which a negative high voltage is applied to a rotary atomizing head formed of a metallic material, and paint is directly electrified with a high voltage through the rotary atomizing head (e.g., Patent Document 3: Japanese Utility Model Laid-Open No. Sho 62-118545 U).
In the electrostatic coating apparatus described in Patent Document 3, an end plate serving as a shaping air ring is provided on the rear side of the rotary atomizing head, and a corona pin is provided on the front surface of the end plate in such a manner as to be located on the radially inwardly of air outlet holes and extend toward a rear surface of the rotary atomizing head. As a negative high voltage is applied to this corona pin, corona ions are supplied to the rear surface side of the rotary atomizing head. Paint particles which approached the rear surface side of the rotary atomizing head are negatively charged by the corona ions. As a result, since the rotary atomizing head and the paint particles which are of the same negative polarity repel from each other, it is possible to prevent the deposition of the paint particles on the rear surface of the rotary atomizing head.